In image display devices such as liquid crystal displays (LCDs), electroluminescence displays (ELDs), field emission displays (FEDs), electric paper, tablet PCs, plasma displays (PDPs), and cathode ray tube displays (CRTs) and in pointing devices such as touch panels, the image display screen is required to reduce reflection of light from external light sources to increase its visibility. An optical layered body in which a hard coat layer and an anti-reflection layer are formed on a light-transmitting substrate is commonly used to reduce reflection on the image display screen and improve the visibility.
A known anti-reflection layer, for example, includes alternating low refractive index layers and high refractive index layers stacked by sputtering or the like on a hard coat layer. The low refractive index layers have a lower refractive index than the hard coat layer and the high refractive index layers have a higher refractive index than the low refractive index layers (see, for example, Patent Literature 1).
In a common image display device including an anti-reflection layer, a hard coat layer and an anti-reflection layer are formed on a light-transmitting substrate, and the light-transmitting substrate is attached to the outermost surface of the image display device.
Production of an optical layered body including such an anti-reflection layer involves formation of a two-layer coating including a low refractive index layer and a high refractive index layer on a hard coat layer. Recent image display devices need three or four or more layers because of demand for a higher anti-reflection function.
Imparting such an anti-reflection function requires repeated sequential coating to stack the low refractive index layer and the high refractive index layer on the hard coat layer.
When the layered body obtained by forming an anti-reflection layer on a hard coat layer is used in an image display device, importance is placed also on the adhesiveness between the hard coat layer, which is mainly made of an organic resin component, and the anti-reflection layer (sputtered layer), which is made of an inorganic component. Techniques thus have been devised for improving the adhesiveness. Known techniques include, for example, a technique of mixing the inorganic component of the anti-reflection layer (sputtered layer) into the resin component of the hard coat layer to improve the adhesiveness, and a technique of forming a SiOx layer as a primer between the hard coat layer and the anti-reflection layer.
The image display devices, however, are being increasingly used outdoors these days, and when the optical layered body is exposed to ultraviolet light outdoors, separation is most likely to occur at the interface between the organic material and the inorganic material. Conventional optical layered bodies thus are disadvantageously susceptible to separation of layers, particularly at the interface between the hard coat layer and the anti-reflection layer.
Since watching various videos is common these days, not only portable tablet PCs but also laptop PCs, which are usually used on a desk or table, are required to provide clearer images. Thus, instead of imparting anti-glare properties as an anti-reflection function, a layered body of a glass-like, clear hard coat layer and an anti-reflection layer is being increasingly used. Such a clear hard coat layer has a smooth outermost surface, so that it has a problem in the surface slipperiness and has poor anti-blocking properties.
The anti-blocking properties affect the ease of winding of the hard coat layer having a smooth surface into a roll and the ease of unwinding during conventionally known polarizing plate processing. In addition, when the anti-reflection layer (inorganic anti-reflection layer) is formed on the hard coat layer by roll-to-roll sputtering or the like in the subsequent step, it is important that the anti-blocking properties are at a level that allows smooth processing even in a vacuum environment.
In a vacuum environment, however, blocking is far more likely to occur than in an atmospheric environment. Layered bodies with a conventional hard coat layer are thus hardly sufficient in anti-blocking properties.